1. Field of the Invention
The present invention relates generally to a method of detecting/identifying organic molecules using electrochemistry and scanning tunneling microscopy, but more particularly to the electrochemically-induced change detection/identification, in situ, of single organic molecules after having been adsorbed on a conducting substrate, e.g., gold or graphite, by use of a scanning tunneling microscope.
2. Description of the Prior Art
It is well known that the scanning tunneling microscope (STM) can be used to identify electronic states on the surfaces of metal or other conducting substrates in an ultrahigh vacuum. The reason for this is that the amount of tunnel current that flows, in otherwise fixed conditions, is a direct measure of the density of electronic states near the Fermi level at the surfaces of the metal or other conducting substrates. As the voltage applied (bias) between the tip of the STM and the surface of a particular metal or other conducting substrate is changed, the energy of the tunneling electrons changes with respect to the energy of the fixed electronic states on the surface, if the bias is applied so that electrons tunnel into the surface. Localized electronic states cause the contrast on the surface of the metal or other conducting substrate to be enhanced as imaged by the STM. The absorption of atoms or molecules onto the surface of the metal or other conducting substrate can, also, give rise to localized surface states which produce features in the STM image which depend on the bias, aforementioned. Spontaneous and charge-induced formation of monolayers of adsorbates of organic molecules on solid surfaces have been widely studied. The STM makes molecular resolution of these adsorbates possible for the first time. As previously mentioned, the STM has been used to study organic adsorbates on metal or other conducting surfaces in an ultrahigh vacuum. In addition, it has been used to image these adsorbates in liquids and in ambient conditions in air. Rather special conditions, however, are required to image such adsorbates, particularly outside an ultrahigh vacuum environment. The organic molecules must form a stable layer which resists the forces encountered in scanning tunneling microscopy while all contamination must be so weakly bound that it is not imaged. Liquid crystals often satisfy these criteria, particularly when the imaging is carried out in a protective layer of the liquid phase. Another approach is to carry out a chemical reaction which binds the molecules to the substrate. This approach relies on the strong STM tip to substrate interaction to "sweep" unwanted molecules away. In general, these methods are quite difficult to carry out in a reproducible way. Even if the adsorbates remain stable, it is highly unlikely that the tip of the associated STM will do so in an uncontrolled environment.
In the more recent past, certain prior art electrochemical methods for control of molecular adsorbates for STM imaging have been explored. The adsorption of organic molecules onto the surface of a metal or other conducting substrate in an ultrahigh vacuum is a very difficult process to control with any specificity and repeatability. Moreover, when the adsorbates are biological molecules, i.e., large organic molecules, control is even more difficult. Hence, methods incorporating ultrahigh vacuum are deemed, as cataloged in the prior art, unsuitable for the analysis of biological molecules.
Consequently, there is a need in the prior art to overcome the foregoing limitations by developing an electrochemically-induced charge method of depositing and holding organic molecules onto the surface of a metal or other conducting substrate where they can be imaged, analyzed and detected/identified, wherein the detection/identification is extended to a single molecule, in situ, by use, inter alia, in combination, of an associated STM.
The prior art, as indicated hereinabove, teach some advances in methods of detecting/identifying organic molecules. Insofar as can be determined, however, no prior art method teaches the detection/identification in an ambient environment (rather than in a vacuum) of a single organic molecule, nor incorporates all of the other features and advantages of the present invention.